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Message |
    
Foxhunter
Junior Member
Username: Foxhunter
Post Number: 24
Registered: 4-2008
| | Posted on Tuesday, July 01, 2008 - 12:52 am: | 
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Hey I just bought two (used--in good condition) Texas Star amps and had a couple of quick questions about them....I have gone to the Texas Star webpage and charts for the "basics" but need a little more about them. Please forgive, I am new to Texas Star.
DX 350HDV---(manufacturer-rated 350W) I understand that the only (?) difference between the DX 350 and the DX 350HDV is the variable (hence "V") output. Is this correct? Why is the HDV called a "high-drive" (HD) if it has the same exact input drive level listed (of 4W-20W) as the plain 350? Also, using the "1:4" or "25%" formula, the "amplified deadkey" should be 87.5 Watts, correct?
DX 500V---(manufacturer rated 500W). "Amplified deadkey" set at 125W using the same above formula?
What is the maximum SAFE voltage that can be applied to either of these amps? I've read before that Texas Star amps do not like to be "volted". Is this true and how much can be used without "red-lining" the amps?
Fankits for these amps. Are they recommended? All amps get hotter with long key-times but are these amps in NEED of fans particularly? If so where on the amp(s) are the fans to be located for maximum effectiveness?
Anything else anyone would add additionally would be greatly appreciated------Foxhunter |
Foxhunter
Junior Member
Username: Foxhunter
Post Number: 25
Registered: 4-2008
| | Posted on Tuesday, July 01, 2008 - 11:42 pm: |
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Hey additionally looking at the RF Parts transistor specifications charts....
The DX 350HDV has 2x 2SC2879's rated at 7W input and 120W output each = only 240W
The DX 500V has 4x 2SC2879's totalling 480W using the same above transistor listings.
Why does Texas Star list 4W-20W drive input on a transistor that is only rated at 7W ? I do understand that the transistor specifications are really "underated" and that they are capable of 125%-150% of their total rated output from what I've read so often. Any Texas Star amplifier owners (or those really familiar with them) out there who really know ? |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2536
Registered: 1-2005
| | Posted on Friday, July 04, 2008 - 10:28 am: |
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The 2879 is a tough transistor. They need at least 7 watts to get them going strong in my opinion. They can handle more. I have never tested them so I can.t say how much more. I do know I can run my 50 watt S-9 with my DX500v with no threat of damage to the amp. Just remember 120 watts per transistor.
Run the amps like this
DX500v-no more than 2 watt deadkey let it swing no more than 50 watts. 40 watts is a good pep btw.
DX350- 2 watts deadkey no more than 20 watts swing MAX.
This usually get the watts in the ballpark of 1:4 power ratio. Little bit of adjust here and there.
NO MORE than 13.8 volts MAX.
Remember- Commercial amps and custom/comp amps are 2 different animals when it comes to watts and volts.
I get 500 watts from my DX 500 and use a fan. It is a good ideal to use a fan if you plan to talk for long peroids.
I have never really understood much of what the Texas Star website has to offer. Maybe because it refers to a CW amp???
KEEP IT REAL!
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
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Foxhunter
Junior Member
Username: Foxhunter
Post Number: 26
Registered: 4-2008
| | Posted on Friday, July 04, 2008 - 11:42 pm: |
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Thanks I appreciate the help. Thank you. What I can't figure out is the Texas Star specifications vs. actual transistor input specifications and their "logic" for their listings as such.
I guess what I've still been wondering and what was the intent of my original posts is:
Firstly: Why does Texas Star list a 4W-20W input level for both of these amps ?(almost all of their amps really) Are they intending/saying a 4W deadkey/carrier with up to 20W swing/PEP ? It lists "input" from 4W-20W. Input usually refers to drive level of course...So is that clearly the case ?
Secondly: That leads me again to my other question: With a transistor such as the 2SC2879 it has listings for input between 5W-7W only (so Texas Stars 4W-20W specification is ALOT different). They are not even close. Why is that ??
Thirdly: Both amps I have the variable knob. Both are listed with the same Texas Star input listing of 4W-20W. So then why is the 350 HDV listed still as a "high drive" amp when it has the same exact input level as the other amps and appears to be just another "low-drive" amp ?? Most real "high-drive" amps really do have a good-sized input/drive level.
I've never owned a Texas Star until recently and saw them demonstrated before I bought them. I've always understood that they don't like "volting" nor are they good for any SWR issues and are really sensitive to SWR levels. I've understood that they really can/do run hot so I was wondering about the fan issue. Unlike a large-cased amp where the fans can be mounted internally I was wondering about fan placement. I have another amp (an older Palomar) that I bought two surplus computer/PC fans at a flea-market and installed them INSIDE the amp to keep the tubes cool. That won't be happening on these small-sized amps so I haven't seen any pic's of fan placement and was wondering what the best mounting scheme would be ?
Hotwire I appreciate your information I WILL keep the voltage on the low-side at 13.8V. I will consider what you've said about the use of the deadkey/swing ratio's you've written here for the 350 & 500. Anything you add is helpful and I appreciate it------Foxhunter |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4323
Registered: 7-2004
| | Posted on Sunday, July 06, 2008 - 7:38 am: |
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1st.....texas star's site is a bit optimistic regarding the output of their amps. and not completely on board with inputs either, in some cases. i wouldn't mind rewriting their 'specs' page. i don't really know why ANY amp has a variable knob....they have a tendancy to burn out when you don't run them full power. your 1st 2 posts show you're right on target, foxhunter! forget about their recommendations. as with ANY amp, once you know the rated output of the transistor, apply sufficient input from radio to get 1/4 of amps output as dead key. so, yes, adjust radio til a dx350 keys about 60 watts. then adjust mic gain til it swings to 240. that's it. any amp. if you have problems with amp, at least you know you didin't overdrive it. forget about ratings, input or output. do it that way & you'll have the best sounding signal out of it. sure, once you add fans (i ALWAYS do), a SMALL increase in dead key is sometimes possible without damage, but swing usually doesn't increase much more. remember, when you increase swing much more then the transistor is rated, things start to sound bad. this is a bit oversimplified-there are exceptions, but for best results, do it this way. texas star amps don't like voltage much above 14 volts, so don't try! |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2540
Registered: 1-2005
| | Posted on Sunday, July 06, 2008 - 2:02 pm: |
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Hey Foxhunter,
A while back Patzerozero taught me a really easy way to attach fans to the Texas Star heatsinks.
Get hold of your little PC cooling fans, the large ones run fine off 12 volts no problem.
On each of the 4 corners of the fan there is a hole used to mount the grille.
Use longer bolts to mount the grille so they stick out about 3/4's of an inch on the other side.
Go to the hardware department at any store and get some plastic drywall anchors. They come in different sizes so you may want to get a variety.
Choose which size drywall anchor fits firmly between the fins of the amps heatsink.
The drywall anchors will screw down onto the bolts sticking out on the fan. I like to glue the anchors onto the bolts for secure grip myself.
You can then push the fan with the anchors into the heatsink fins and it will stay there.
I've been doing it like this for a few years now and it works perfect!
Also, I prefer to push air into the heatsink. Some prefer to pull the air though the heatsink.
Both ways should work just fine.
KEEP IT REAL!
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
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Drzuo
Junior Member
Username: Drzuo
Post Number: 18
Registered: 1-2006
| | Posted on Sunday, July 06, 2008 - 8:29 pm: |
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I've seen a lot of posts with confusion on transistor output and drive ratings, maybe I can help.....I'll use the 2sc2879 for an example. The newer spec sheet rates the device 120 watts output and a maximum drive of 10 watts pep. An amp that uses a pair may have different in/out specs that you would expect to get from multiplying the number of transistors by the spec sheet ratings. In the spec sheets the transistor is being tested at(a) 28mhz, (b) 12.5 volts (c) class a/b (d) single ended (one transistor) in a (e) broadband circuit.
so I'll attack all these little things one at a time.
(a) The transistor is more efficient and will have a slightly higher output capability the lower it goes ie 27mhz instead of 28mhz
(b) The transistor will have a higher output as the voltage is increased ie 12.5 v to 13.8 or more
(c) A class c amp will take more drive than a class ab amp because there is no bias voltage applied to the transistor like there is in an a/b amp.
(d)2 transistors in a push pull circuit is more efficient and cleaner than a single ended amp of the same design (every other harmonic is cancelled out)hence a slight increase in power output for the same spectral purity can be achieved (if well designed.)
(e) matching circuits can be designed with a higher q to reduce bandwidth but increase gain.
Also remember that 10 watts of drive is what the transistor expects to see, not what the coax connector gets. the signal, once it leaves the radio has to go thru a filter, a transformer, some routed to a keying circuit, some padding, and even the final bias resistors( the 10 ohm ones from base to ground) which will devert some power. Not too mention that your match(swr's) between the radio and amp might be as high as a 2:1(or more) easily knocking down that 25 watts leaving the radio to 20 watts by the time it reaches the transistor. Transformers can also be wrapped to different ratios and padded with resistors and capacitors and other components to compensate for the impedance mismatch, so the radio sees close to 50 ohms, but the amp can take drive levels to operate within just about any parameters the manufacturers wish. ( remember those little boxes that you used to hook to your car stereo speaker outputs and converted it to rca cables to run an amp?)
So will a pair of 2879's do 800 watts? I wouldnt bet on it. 300-350 watts? In a well designed amp I'd say yes. Also remember its not only about the power, but stability and spectral purity.
There are other factors that can affect the power output too, these are some of the basics, hope this helped. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 4325
Registered: 7-2004
| | Posted on Sunday, July 06, 2008 - 10:48 pm: |
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'Also, I prefer to push air into the heatsink. Some prefer to pull the air though the heatsink'-if the amp is BIG enough, i'll use multiple fans in BOTH push & pull configuration  |
Foxhunter
Junior Member
Username: Foxhunter
Post Number: 31
Registered: 4-2008
| | Posted on Wednesday, July 09, 2008 - 9:58 pm: |
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OK---Hat's off to you Hotwire, Pat Z and Drzuo this is really great because I can't think of any further questions as they have all been answered. I'll generally stick to the 1:4 drive ratio as that is a good practice I believe. Hotwire your explanation of the fan install method that Pat had passed to you is excellent and I will be doing precisely that. Pat you should write/have an "alternative Texas Star webpage/user guide" as I believe you're right on the mark with these operation set-up procedures. Hotwire you are of the same school-of-thought and the explanation is good. Drzuo your breakdown of the additional considerations associated with the input signal levels and how they might be affected by particular amplifier design and the resulting differences in outcome. I will be definitely be saving this posting for future reference as well as your explanations all were of good-quality. I wish I could return the favor somehow as I really do appreciate the advice. Thank You!-----Foxhunter |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2545
Registered: 1-2005
| | Posted on Friday, July 11, 2008 - 11:09 am: |
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Glad to be a help Foxhunter. Just get on the air and give me a shout. In the evenings I've had the direct line to Jersey, almost all week long!73!
KEEP IT REAL!
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
|
Foxhunter
Member
Username: Foxhunter
Post Number: 52
Registered: 4-2008
| | Posted on Monday, July 21, 2008 - 11:45 pm: |
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Hey sorry I didn't reply back. Indiana? Spent many-a-night out there, often in the Gary area (!!!!) but quite a number of other places too. I'll be up and running soon......
What's the calling frequency?? Hey thanks for your help----and with the help in other threads you've given me. Thanks------Foxhunter |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2549
Registered: 1-2005
| | Posted on Wednesday, July 23, 2008 - 12:06 pm: |
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All Copper members standby on 27.115 AM channel 13 and sometimes we can be found standing by on LSB.
During heavy skip I can be found there in the evenings between 5pm and 9pm EST.
KEEP IT REAL!
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
|
Foxhunter
Member
Username: Foxhunter
Post Number: 60
Registered: 4-2008
| | Posted on Thursday, July 24, 2008 - 7:12 pm: |
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Now that I'm getting set-up here at home I will finally be able to check out our Copper member's calling frequencies then--------Thanks Hotwire
Foxhunter |
